<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<style type="text/css">
.active{
color:red;
border:3px solid blue;
}

</style>
</head>
<body>

<div class="active">Hello World!</div>
<div id="target">Hello World!</div>
<script type="text/javascript">
document.getElementById("target").setAttribute("class", "active");
</script>
</body>
</html>